1. Field of the Invention
The present invention concerns a mechanism that can be used, in particular, for a sonar antenna, and comprises a support, an arm and a connecting rod, the arm and the connecting rod being movable in parallel planes, a driving device to give a translational motion along two opposite directions so that, by mechanical coupling, the arm is made to go from the "lowered arm" position to the "outstretched arm" position and vice versa, a first, second and third "rotation pin", namely a pin defining an axis of rotation around which one or more parts may rotate, said rotation pins being perpendicular to the parallel planes and acting, respectively, as rotation pins for the first end of the connecting rod, the second end of the connecting rod and the first end of the arm, and for the arm at a point of the arm located at a given distance from its first end.
2. Description of the Prior Art
Such mechanisms are known, and an embodiment of one of these known mechanisms shall be described with the help of FIGS. 1a and 1b. As shall be seen from the description of these figures, the known mechanisms drive a simple pivoting motion of the arm between two extreme positions, namely the "lowered arm" and "outstretched arm" positions, without enabling the arm to be kept, reliably, in the "lowered arm" position. Now it turns out that, in certain applications, for reasons related to the protection of equipment exposed to harsh environmental conditions, it is useful to have a system for properly locking the arm in the lowered position, that is, a locking system capable of withstanding vibrations and even lateral tugging forces.